The growth-differentiation balance hypothesis (GDBH) predicts changes in susceptibility of plants against herbivores with changing resource availability. In the presented study we tested the validity of the GDBH for trees infected with a root pathogen. For this purpose Fagus sylvatica seedlings grown under different atmospheric CO2- and soil nitrogen regimes were infected with the root pathogen Phytophthora citricola. High nitrogen supply increased total biomass of beech regardless of the CO2-treatment, whereas elevated CO2 enhanced biomass only in the high nitrogen treatment. The responses of beech under the different growing regimes to the Phytophthora root infection were not in line with the predictions of the GDBH. Enhanced susceptibility of beech against P. citricola was found in seedlings grown under elevated CO2 and low nitrogen supply. Fifteen months after inoculation these plants were characterized by enhanced water use efficiency, by altered root–shoot ratios, and by enhanced specific root tip densities.

Root respiration has been shown to increase with temperature, but less is known about how this relationship is affected by the fungal partner in mycorrhizal root systems. In order to test respiratory temperature dependence, in particular Q (10) of mycorrhizal and non-mycorrhizal root systems, seedlings of PICEA ABIES (L.) Karst. (Norway spruce) were inoculated with the ectomycorrhizal fungus PILODERMA CROCEUM (Eriksson and Hjortstam, SR430; synonym: PILODERMA FALLAX: [Libert] Stalpers) and planted in soil respiration cuvettes (mycocosms). Temperature dependence of hyphal respiration in sterile cultures was determined and compared with respiration of mycorrhizal roots. Respiration rates of mycorrhizal and non-mycorrhizal root systems as well as sterile cultures were sensitive to temperature. Q (10) of mycorrhizal root systems of 3.0 +/- 0.1 was significantly higher than that of non-mycorrhizal systems (2.5 +/- 0.2). Q (10) of P. CROCEUM in sterile cultures (older than 2 months) was similar to that of mycorrhizal root systems, suggesting that mycorrhizae may have a large influence on the temperature sensitivity of roots in spite of their small biomass. Our results stress the importance of considering mycorrhization when modeling the temperature sensitivity of spruce roots.

DNA-based quantification methods such as real-time TaqMan PCR allow a rapid and highly sensitive species-specific quantification of isolated fungal DNA material, but most quantification systems are only able to measure relative amounts of biomass or biomass changes during different treatments. In this experiment, an already established DNA quantification system for the ectomycorrhizal fungus Piloderma croceum, based on the ITS region of ribosomal DNA, was calibrated to absolute biomass to obtain a direct correlation between mycelial biomass and isolated ITS copies. Thin layers of sterile mycelia were cultured on slides. The mycelial biomass was calculated from measurements of the total hyphal length using image analysis, followed by determination of the mycelial volume, and multiplied by the specific weight of hyphae obtained from literature data. Using the very same mycelium, the number of ITS copies was quantified by TaqMan PCR. The mean value of 1047 (+/- 185) copies per mm hypha results in possible data for a direct conversion: one billion (10 (9)) ITS copies corresponded to 0.79 mg hyphal dry weight. For the ribosomal ITS multi-copy genes, the number of ITS copies could be calculated to approx. 152 (+/- 26) copies per dikaryotic cell. These conversion data now allow determination of the mycelial biomass of Piloderma croceum using real-time TaqMan PCR, a prerequisite for competition experiments with Piloderma croceum.

A microplate fluorimetric assay was developed for measuring potential activities of extracellular enzymes of individual ectomycorrhizal (EM) roots using methylumbelliferone (MU)-labelled fluorescent substrate analogues and microsieves to minimise damage due to manipulation of excised mycorrhizal roots. Control experiments revealed that enzyme activities remained stable over the whole time of the experiment suggesting a strong affinity of the studied enzymes to the fungal cell walls. The same mycorrhizal tips thus could be used repeatedly for enzyme detection and subsequently analysed for the projection area by automated image analysis. The developed system was evaluated on four different EM species measuring pH optimum and substrate saturation of phosphatase, chitinase and β-glucosidase. The four EM species studied were Lactarius subdulcis, Russula ochroleuca, Cortinarius obtusus and Xerocomus cf. chrysenteron. Depending upon the enzyme, each species exhibited different levels of enzymatic activities as well as enzyme kinetics and showed also differences in pH optima.

The rhizomorphal ontogeny of Hydnum rufescens, Laccaria amethystina and Sarcodon imbricatus are comprehensively described and compared. Laccaria amethystina forms undifferentiated rhizomorphs composed of hyphae of nearly identical diameter. Most septa of the hyphae are clamped, backwards growing hyphal branches are lacking. Three different types of anastomoses could be found: the first type starts with an anastomosis of a hyphal apex with a lateral part of a neighbouring hypha, a reversely oriented clamps is formed within the anastomosing hypha and beneath this clamp a new side-branch grows out into the same direction as the hyphal apex, finally a rather long hyphal bridge possessing a clamp results; the second type is also characterized by an anastomosis of a hyphal apex with a lateral part of another hypha and the formation of a reversely oriented clamp, but in contrast to the first type further development is characterized by continued hyphal growth above the reversely oriented clamp and the formation of one or more simple septa, after which the hypha again forms clamps; in the third type a hypha forms a subapical anastomosis with a lateral part of a neighbouring hypha, but a reversely oriented clamp will not be formed, the hypha continues to grow forming some simple septa and thereafter clamps. The rhizomorphs of Sarcodon imbricatus are slightly differentiated. They develop some thicker, irregularly distributed hyphae. Both the thin and the thick hyphae possess clamps and simple septa. Anastomoses are frequent, approximately half of them have a contact-septum. Backwards growing side-branches occur; they mostly originate above the first clamp of a hyphal sidebranch, very in-frequently above a clamp independently of a branching point. In addition to characteristically formed chlamydospores, clusters of hyphae may occur. The rhizomorphs of Hydnum rufescens are slightly differentiated with hyphae which can be inflated at their clamps, resulting in a trumpet-like shape. The frequently occurring anastomoses may possess clamps. Backwards growing hyphae occur mostly originating above the first clamp of a sidebranch. Hyphae growing in parallel but towards one another can be distinctly intertwined. Clusters of hyphae can be formed similar to those found in Sarcodon imbricatus.